The effect of RF inhomogeneity on heteronuclear dipolar recoupling in solid state NMR: Practical performance of SFAM and REDOR

Practical heteronuclear dipolar recoupling performances under magic angle s pinning for SFAM and REDOR have been investigated under well-defined rf inh omogeneity environments with variation of resonance offsets for the irradia ted nucleus. The heteronuclear dipolar recoupling efficiencies were quantit atively determined based on the experimentally obtained rf homogeneity. As a result, SFAM retains higher recoupling efficiency (>95%) at an 85% effect ive nutation frequency, and its recoupling efficiency is gradually reduced at lower effective nutation frequencies. On the other hand, although REDOR retains higher recoupling (>95%) efficiency at high (>92%) effective nutati on frequency with an XY-8 compensation pulse sequence, the recoupling effic iency is dramatically decreased when the effective nutation frequency is be low 90%. Over all, SFAM has significant advantages for insensitivity to car rier frequency offset and rf inhomogeneity. (C) 2001 Academic Press.